JP2001201573A - Coherent laser radar device and target measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the device to reduce the cost. SOLUTION: The pulse laser beam from a pulse laser 1 is branched to two beams by a light branching device 2. One of the branched beams is transmitted as transmission beam to a target through a beam splitter 3 or the like as transmission beam. The other beam is delayed as local beam by a prescribed time in a delay line 11 and incident on an optical coupler 8 through a coupling optical system 9 or the like. The received beam from the target is incident on the optical coupler 8 through a scanning optical system 6 or the like. The beam coupled by the optical coupler 8 is coherent detected by an optical wave detector 12, and the speed or the like of the target is calculated by a signal processor 14 on the basis of the signal generated by the wave detection and A/D converted by an A/D converter 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coherent laser radar apparatus and a target measuring method for measuring physical information such as a distance, a velocity, a density distribution and a velocity distribution of a target, and more particularly to a pulse of a single wavelength (single frequency). The present invention relates to a coherent laser radar device using a pulse laser that oscillates laser light as a light source and a target measuring method.

[0002]

2. Description of the Related Art As a device for measuring physical information such as a target distance, speed, density distribution, and speed distribution, a pulse Doppler radar device using a microwave or a millimeter wave and a light wave (laser light) are used. There is a coherent laser radar device to be used. Due to the difference between the two frequencies, the former can measure over a wide range and a long distance, and the latter can measure with high spatial resolution and high speed resolution.

In the measurement of wind speed and wind speed distribution, etc., which are targets of a soft target, a pulse Doppler radar apparatus mainly uses raindrops, fog or cloud particles in the atmosphere as scatterers, and calculates the wind speed from the Doppler shift of the echo. I do. Therefore, there is a drawback that echoes of sufficient intensity cannot be obtained in fine weather when there are no raindrops, fog or cloud particles in the atmosphere, and it is difficult for the pulse Doppler radar device to measure turbulence in fine weather.

On the other hand, a coherent laser radar device using a laser beam can obtain a sufficient scattering intensity even with aerosol in the atmosphere, so that the wind speed and the wind speed distribution can be measured even in fine weather. For this reason, a coherent laser radar device is expected to be installed at an airport or mounted on an aircraft to detect an obstacle such as turbulence. Such a coherent laser radar device uses a pulse laser that oscillates a single-frequency pulsed laser beam as a light source, and a CW (Continuous) that oscillates a single-frequency continuous light beam.
uuous Wave) laser is used as a light source.

FIG. 16 shows, for example, US Pat. No. 5,237,33.
FIG. 1 is a block diagram illustrating a configuration of a conventional coherent laser radar device described in No. 1. In this conventional coherent laser radar device, an injection seeding pulse laser is used as a light source.

In FIG. 1, reference numeral 101 denotes a CW laser light source that oscillates CW laser light at a single frequency, and 102 denotes a CW laser light source.
An optical splitter for splitting a part of the laser light as local light, a frequency shifter 103 for shifting the frequency of the CW laser light, and an injection seeding 104 for generating a pulse laser light using the CW laser light as a seed light Reference numeral 105 denotes a pulse laser. Reference numeral 105 denotes an optical splitter that splits the pulse laser light. Reference numeral 106 denotes a light that reflects the light from the optical splitter 105 by using a difference in polarization direction, and is 1/4.
The beam splitter 107 transmits light from the wave plate 107. The beam splitter 107 converts linearly polarized light having a predetermined polarization direction with respect to the crystal axis into circularly polarized light, and converts circularly polarized light into linearly polarized light.
A 波長 wavelength plate 108 transmits and receives light from the ４ wavelength plate 107 to the scanning optical system 109 and supplies light from the scanning optical system 109 to the 波長 wavelength plate 107 along the same optical path. An optical system 109 is a scanning optical system that transmits transmission light toward a target and receives scattered light from the target as reception light.

Reference numeral 110 denotes an optical splitter for splitting local light, and 111 denotes an optical coupler for coupling the local light split by the optical splitter 110 and the pulse laser light split by the optical splitter 105. 112 is an optical splitter 110
Beam splitter 106 and the local light split by the
And an optical coupler that couples the received light transmitted through
Is an optical detector for detecting the light coupled by the optical coupler 111, 114 is an optical detector for detecting the light coupled by the optical coupler 112, and 115 is an optical detector 113,
A / D converters for converting the electric signals detected and generated by 114 into digital signals, respectively.
This is a signal processing device that calculates physical information such as a target distance, speed, density distribution, and speed distribution based on two detection signals converted into digital signals by the D converter 115.

A control circuit 117 controls the adjusting mechanism 118 based on a signal from the signal processing device 116.
18 is an injection seeding pulse laser 10
4 is an adjustment mechanism such as a piezo element for adjusting the resonator length.

FIG. 17 is a block diagram showing a configuration example of a signal processing device 116 of a conventional coherent laser radar device. In the figure, reference numeral 121 denotes a storage device such as a memory for temporarily storing a digital signal from the AD converter 115, and 122 denotes a digital signal stored in the storage device 121 for receiving light from a certain distance range. A time gate unit for selecting a corresponding digital signal. Reference numeral 123 denotes a Hanning process or a Hamming process.
g) a window processing unit that executes window processing such as processing, and 124 denotes an FFT that executes fast Fourier transform
Reference numeral 125 denotes a Doppler frequency detection unit that detects a Doppler frequency based on the Fourier-transformed signal.

Next, the operation will be described. FIG. 18 is a timing chart for explaining the operation of the conventional coherent laser radar device.

The CW laser light source 101 oscillates CW laser light at a single frequency f ₀ (ie, at a single wavelength) and supplies it to the optical splitter 102. The optical splitter 102 splits the CW laser light into two. One of the two branched CW laser lights is a local light, and the other is a frequency shifter 103.
Supplied to The local light is further split into two by the optical splitter 110 and supplied to the optical couplers 111 and 112, respectively. On the other hand, the frequency shifter 103 increases the frequency the frequency of the CW laser light by frequency _{f IF,} the frequency f
The CW laser light of ₀ + f _IF is supplied to the injection seeding pulse laser 104 as seed light.

The injection seeding pulse laser 104 oscillates pulse laser light of a single frequency (ie, a single wavelength) in the axial mode of the frequency closest to the frequency of the seed light. The pulse laser light from the injection seeding pulse laser 104 is partly branched by the optical branching device 105 and then enters the beam splitter 106. Part of the pulsed laser beam split by the optical splitter 105 enters the optical coupler 111.

The pulse laser light from the injection seeding pulse laser 104 is linearly polarized light having a predetermined polarization direction, is reflected by the beam splitter 106,
The light is incident on the 波長 wavelength plate 107. And 1/4 wavelength plate 1
After being converted into circularly polarized light by 07, the pulsed laser light is transmitted to a target as transmission light via a transmission / reception optical system 108 and a scanning optical system 109.

[0014] The pulsed laser light thus transmitted to the target is scattered by the target, and a part of the scattered light enters the scanning optical system 109.

The scattered light from the target, which is the received light, travels in the same optical path as the transmitted light in the scanning optical system 109 and the transmitting / receiving optical system 108 in the opposite direction, and enters the quarter-wave plate 107. The received light is converted into linearly polarized light having a polarization direction rotated by 90 degrees from the polarization direction of the pulse laser light by the 波長 wavelength plate 107, and is incident on the beam splitter 106.

The beam splitter 106 transmits the received light and supplies it to the optical coupler 112. The optical coupler 112 combines the received light and the local light, and supplies the combined light to the optical detector 114. The optical detector 114 coherently detects the combined light, and converts the electric signal generated by the detection into an A signal.
It is supplied to the D converter 115.

On the other hand, the optical coupler 111 combines the pulse laser beam split by the optical splitter 105 with the local light, and supplies the combined light to the optical detector 113. The optical detector 113 performs coherent detection of the combined light and supplies an electric signal generated by the detection to the AD converter 115.

The electric signals from the optical detectors 113 and 114 are sampled by an AD converter 115 and supplied to a signal processing device 116 as digital signals. Based on the signal from the optical detector 114, the signal processor 116 calculates a target distance from a time waveform of the intensity of the signal, and calculates a target speed from a Doppler signal component of the signal.

The frequency of the local light must maintain a constant relationship with the frequency of the pulsed laser light during this sampling for accurate measurement. That is, CW
The laser light source 101 is required to have frequency stability. For example, if the CW laser beam having a wavelength of 2 micrometers is local light, the maximum measurement distance is 15 km, and the measurement error of the target speed is 0.1 m / s or less, 0.1
The frequency variation of the CW laser light during 100 milliseconds
It must be below kilohertz. Therefore, in order to realize such frequency stability, the CW laser has a more complicated configuration, a wavelength is appropriately selected, and temperature stability or power source stability is ensured.

In the signal processing device 116, the AD converter 11
A signal (beat signal shown in FIG. 15) corresponding to the combined light of the received light and the local light sampled by 5 is stored in the storage device 121. The time sampled by the AD converter 115 is the time from the pulse oscillation until the scattered light from the target located at the maximum measurement distance is received.

The time gate unit 122 obtains information on a target within an arbitrary distance range.
The portion including the scattered light from the target among the sampling signals accumulated in 1 is extracted, and the window processing unit 123
Supplied to The window processing unit 123 performs window processing on the sampling signal in order to improve frequency measurement accuracy. Thus, a signal having a waveform as shown in FIG. 15 is obtained.

The FFT unit 124 calculates the frequency spectrum of the signal after the window processing, and the Doppler frequency detection unit 125 detects the Doppler frequency to calculate the target speed.

In this way, the target speed and the like are measured by the conventional coherent laser radar device.

The signal from the optical detector 113 is used to improve the accuracy of calculating the target distance and speed.
As described above, the injection seeding pulse laser 4 oscillates in the axial mode of the frequency closest to the frequency of the seed light. Therefore, in order to obtain an accurate Doppler signal, the frequency difference between the pulse laser light and the local light is monitored. There is a need to. Therefore, a part of the pulse laser light and a part of the local light are respectively taken out by the optical splitters 105 and 110, and the light obtained by combining the two by the optical coupler 111 is coherently detected by the optical detector 113. Then, the detected signal is sampled by the AD converter 115 in the same manner as the received light, the frequency difference between the pulse laser light and the local light is calculated by the signal processing device 116, and the pulse is sent to the control circuit 117 based on the calculation result. A signal for controlling the frequency of the laser light is supplied.

Here, the frequency of the local light is represented by f₀To be
And seed light, pulsed laser light, received light, frequency monitor
Frequency f of signal and received signal_S, F_T, F_R, F_M,
f_{si g}Are as shown in the following equations. f_S= F₀+ F_IF  f_T= F_S+ Δf f_R= F_T+ F_d  f_M= F_IF+ Δf f_sig= F_M+ F_d  Here, Δf is the frequency difference between the pulse laser light and the seed light.
And f_dIs the target Doppler frequency. Also, the frequency
The monitor signal stabilizes the oscillation frequency of the pulsed laser light.
Used to

Therefore, the target Doppler frequency f
_d is the difference between the frequency f _sig of the received signal and the frequency f _M of the frequency monitor signal.

In order to stably execute the injection seeding operation, the frequency of the pulse laser light is adjusted by controlling the adjusting mechanism 118 to adjust the cavity length of the injection seeding pulse laser 104. The signal processing device 116 supplies a frequency difference Δf between the pulse laser light and the local light to the control circuit 117 based on the frequency f _M of the frequency monitor signal. The control circuit 117 adjusts the resonator length of the injection seeding pulse laser 104 by controlling the adjusting mechanism 118 so that the value of the frequency difference Δf is equal to or less than a predetermined set value or 0, and adjusts the frequency of the pulse laser light. To adjust.

In this manner, a stable single mode (single wavelength) pulse laser beam can be obtained from the injection seeding pulse laser 104.

[0029]

Since the conventional coherent laser radar device is configured as described above, a CW laser is provided as a local light source in addition to a pulse laser for generating transmission light in order to perform coherent detection. And the CW laser has a single frequency CW
Since the laser light needs to oscillate with high frequency stability, the CW laser itself has a complicated configuration, and further, it is necessary to provide a mechanism for monitoring the frequency difference between the transmission pulse laser light and the local light, and the device is complicated. However, there is a problem that it is difficult to reduce the cost, reduce the size, and increase the reliability.

The present invention has been made to solve the above problems, and transmits and receives a single-frequency (single-wavelength) pulse laser beam to and from a target, and transmits a part of the pulse laser beam. The light is delayed and combined with the received light, and the combined light is coherently detected. Thus, there is no need to provide a CW laser light source or a mechanism for monitoring the frequency difference between the transmitted pulse laser light and the local light, and has a simple configuration. It is an object of the present invention to obtain a low-cost, compact, and highly reliable coherent laser radar device.

[0031]

A coherent laser radar device according to the present invention transmits a pulse laser beam oscillating a single-wavelength pulse laser beam and a pulse laser beam oscillated by the pulse laser toward a target. A transmitting / receiving optical system for receiving scattered light from a target as received light, an optical branching unit for branching a part of the pulsed laser light oscillated by the pulsed laser, and a part of the pulsed laser light branched by the optical branching unit. A delay means for delaying, a light coupling means for coupling a part of the pulsed laser light delayed by the delay means with the received light, a light detection means for coherently detecting the light coupled by the light coupling means, and a light detection means. A signal processing device that specifies target physical information based on the coherently detected signal.

In the coherent laser radar device according to the present invention, the delay means is a delay line composed of an optical fiber having a predetermined length.

The coherent laser radar device according to the present invention comprises an optical splitter for splitting a part of the pulse laser light split by the optical splitting means into n light beams, and an optical splitter for splitting the n light beams having different delay times. The delay means includes n number of delay lines for delaying the respective light beams by only N and a light coupler for coupling the n number of lights delayed by the n number of delay lines.

The coherent laser radar device according to the present invention introduces a loop line for transmitting laser light, a part of the pulse laser light branched by the optical branching means into the loop line, and a laser light in the loop line. And an optical coupler that branches the light into the delay means.

The coherent laser radar device according to the present invention has an optical amplifier in the middle of the loop line of the delay means.

The coherent laser radar device according to the present invention includes an optical amplifier for amplifying local light between the delay unit and the optical coupling unit.

In the coherent laser radar device according to the present invention, the optical amplifier is an optical fiber amplifier.

In the coherent laser radar device according to the present invention, the optical amplifier is a semiconductor optical amplifier.

In the coherent laser radar device according to the present invention, the optical amplifier is a solid-state laser medium laser amplifier.

In the coherent laser radar device according to the present invention, the optical coupler is a variable optical coupler having a variable branching ratio.

The coherent laser radar device according to the present invention includes an optical switch of a photoacoustic optical element for outputting one of a part of the pulse laser beam branched by the optical branching unit and the light in the loop line to the loop line. And an optical splitter for splitting light in the loop line in the optical coupler.

The target measurement information according to the present invention includes a step of oscillating a single-wavelength pulsed laser beam, a step of branching a part of the pulsed laser light, a step of sending the pulsed laser light toward the target, and a step of transmitting the pulsed laser light from the target. Receiving the light as received light, delaying a part of the branched pulse laser light, combining the delayed pulse laser light with the received light, and coherently detecting the combined light, Identifying physical information of a target based on the coherently detected signal.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a block diagram showing a configuration of a coherent laser radar device according to Embodiment 1 of the present invention. In the drawing, reference numeral 1 denotes a pulse laser that oscillates a pulse laser beam of a single frequency (single wavelength), 2 denotes an optical splitter (optical splitting unit) that splits a part of the pulse laser beam, and 3 denotes polarization. 4 is a beam splitter that separates the optical path between the transmitted light and the received light using the difference in direction, and 4 is a linear polarized light having a predetermined polarization direction with respect to its crystal axis, and a circular polarized light. １ ／ wavelength plate for conversion, 5
Supplies the light from the quarter-wave plate 4 to the scanning optical system 6 along the same optical path, and also reduces the light from the scanning optical system 6 to 1/4.
A transmission / reception optical system 6 supplies the wavelength plate 4 with a transmission optical system 6. The transmission optical system 6 transmits transmission light toward a target and receives scattered light or reflected light from the target as reception light. The transmission / reception optical system 5 and the scanning optical system 6 constitute transmission / reception optical means for transmitting pulsed laser light oscillated by the pulse laser 1 toward a target and receiving light from the target as reception light.

Numeral 7 is a coupling optical system for making the light received from the beam splitter 3 incident on the optical coupler 8, and 8 is an optical coupler (light) for coupling the received light with the frequency-shifted and delayed pulse laser light. 9 is an optical splitter 2
Is a coupling optical system that causes the pulsed laser light branched by (1) to enter the frequency shifter 10, a frequency shifter 10 that increases the frequency of a part of the branched pulsed laser light by a predetermined frequency, and 11 is a predetermined time. This is a delay line (delay means) for delaying the laser light only.

Reference numeral 12 denotes an optical detector (optical detector) for coherently detecting the light coupled by the optical coupler 8.
Reference numeral 3 denotes an AD converter that converts an electric signal detected and generated by the optical detector 12 into a digital signal. Reference numeral 14 denotes a signal processing for specifying physical information such as a target speed and distance based on the coherently detected signal. Device.

FIG. 2 is a block diagram showing an example of the configuration of the signal processing device of FIG. In FIG. 2, reference numeral 21 denotes a storage device such as a memory for temporarily storing a digital signal from the AD converter 13; and 22, a digital signal stored in the storage device 21 and a receiving light from a certain distance range. Is a time gate unit for selecting a digital signal corresponding to
Is an FFT unit that executes fast Fourier transform, and 24 is a Doppler frequency detection unit that detects a Doppler frequency based on the Fourier-transformed signal.

FIG. 3 is a block diagram showing another example of the configuration of the signal processing device of FIG. In FIG. 3, reference numeral 25 denotes a time gate unit that operates the AD converter 13 only during a period corresponding to received light from a certain distance range.

Next, the operation will be described. FIG. 4 is a timing chart for explaining the operation of the coherent laser radar device according to the first embodiment. The target at this time is a soft target such as the atmosphere.

The pulse laser 1 has a single frequency (single wavelength)
Oscillates pulsed laser light. The pulse laser light is split into two by the optical splitter 2, and one of the split light is incident on the beam splitter 3, and the other is incident on the frequency shifter 10 via the coupling optical system 9 as local light. In addition,
The local light travels through the optical fiber coupled to the coupling optical system 9 and enters the frequency shifter 10. Frequency shifter 10
The local light whose frequency has been increased by a predetermined intermediate frequency enters the delay line 11. After delaying the local light by a predetermined time, the delay line 11
Incident on

The pulse laser beam incident on the beam splitter 3 passes through the beam splitter 3 and is incident on the quarter-wave plate 4. After being converted into circularly polarized light by the 波長 wavelength plate 4, the pulsed laser light is transmitted to the target as transmission light via the transmission / reception optical system 5 and the scanning optical system 6.

The pulsed laser beam sent to the target in this way is scattered or reflected by the target, and a part of the scattered light or reflected light enters the scanning optical system 6.

The light from the target, which is the received light, travels in the same optical path as the transmitted light in the scanning optical system 6 and the transmitting / receiving optical system 5 in the opposite direction, and enters the quarter-wave plate 4. Received light is 1
The light is converted into linearly polarized light having a polarization direction rotated by 90 degrees from the polarization direction of the pulse laser light by the 波長 wavelength plate 4 and is incident on the beam splitter 3.

The beam splitter 3 reflects the received light having a polarization direction different from that of the pulse laser light, and the received light enters the optical coupler 8 via the coupling optical system 7. The received light travels through the optical fiber coupled to the coupling optical system 7 and enters the optical coupler 8. The optical coupler 8 combines the received light with the local light from the delay line 11 and supplies the combined light to the optical detector 12. The optical detector 12 performs coherent detection (optical heterodyne detection) of the combined light, and supplies an electric signal generated by the detection to the AD converter 13.

The electric signal from the optical detector 12 is sampled by the AD converter 13 and supplied to the signal processing device 14 as a digital signal. The signal processing device 14 calculates a target speed or the like based on a signal from the optical detector 12.
At this time, the target measurement distance is determined by the delay time of the delay line 11. That is, only the target whose distance from the transmission of the transmission light to the reception of the reception light is substantially equal to the delay time is measured.

If the signal processing device 14 is as shown in FIG. 2, for example, as shown in FIG.
The signal (beat signal shown in FIG. 4) corresponding to the combined light of the received light and the local light sampled by the above is stored in the storage device 21. The frequency of the beat signal at this time is the sum of the intermediate frequency and the Doppler frequency. Note that a beat signal is obtained only when local light, which is pulsed laser light, is present.

Then, a portion including the beat signal is extracted from the sampling signal stored in the storage device 21 by the time gate section 22, the frequency spectrum of the signal is calculated by the FFT section 23, and the Doppler frequency is detected by the Doppler frequency detection section 24. To calculate the target speed.

Since the local light is a pulsed laser light, the electric signal after detection also has a pulse shape, and the same processing as the window processing in the conventional apparatus is not required. Therefore, the apparatus can be further simplified. it can.

When the signal processing device 14 is as shown in FIG. 3, the time gate unit 25 operates the AD converter 13 only during the time when the local light is received by the optical detector 12, and the time gate 25 Only the beat signal is supplied to the FFT unit 23. Therefore, by making the signal processing device 14 as shown in FIG. 3, the storage device 21 such as a memory can be omitted, and the device can be further simplified.

As described above, according to the first embodiment, a single-frequency pulsed laser beam is transmitted / received to / from a target, and a part of the pulsed laser beam is delayed and combined with the received beam. Since the combined light is coherently detected, there is no need to provide a CW laser light source or a mechanism for monitoring the frequency difference between the transmission pulse laser light and the local light, thereby simplifying the configuration of the apparatus, and Accordingly, the effect that cost reduction, size reduction, and high reliability can be achieved is obtained.

The delay line 11 is made of, for example, a long optical fiber. The delay time can be easily set by the length of the optical fiber, and a small and low-loss delay line can be obtained by winding the optical fiber around a reel.
The effect that the scale of an apparatus can be reduced is obtained. Also, by using a polarization maintaining optical fiber,
The change in the polarization state of the local light can be reduced.

In the first embodiment (FIG. 1),
The optical splitter 2 for extracting a part of the pulse laser light is provided outside the resonator of the pulse laser 1. However, the optical component in the resonator has the function of the optical splitter 2 so that a part of the pulse laser light can be obtained. The same effect can be obtained by extracting.

Embodiment 2 FIG. 5 is a block diagram showing a configuration of a delay line of a coherent laser radar device according to Embodiment 2 of the present invention. Delay line 11 shown in FIG.
In the formula, the reference numeral 31 denotes n incident local lights (n>
It is an optical splitter that splits into light of 1), 32-1 to 32-32.
n is an n-number of delay lines that delay the n-pieces of divided light by different delay times, and 33 is an optical coupler that combines the n-number of lights delayed by the n-number of delay lines.

The other components of the coherent laser radar device according to the second embodiment are the same as those according to the first embodiment (FIG. 1), and thus description thereof will be omitted.

Next, the operation will be described. FIG. 6 is a timing chart for explaining the operation of the coherent laser radar device according to the second embodiment. The target at this time is a soft target such as the atmosphere.

In the delay line 11 according to the second embodiment, the optical splitter 31 and the optical coupler 33 are connected by n delay lines 32-1 to 32-n having different delay times.
Thereby, as shown in FIG. 6, local light having n pulses is generated from a part (single pulse) of the pulsed laser light. FIG. 6 shows, as an example, local light when the difference in delay time between the delay line 32-i and the delay line 32- (i + 1) is twice the pulse width τ. Note that the other operations are the same as those in the first embodiment, and a description thereof will be omitted. However,
The time gates 22 and 25 of the signal processing device 14 extract a beat signal corresponding to each pulse of the local light according to the time position of each pulse of the local light and supply the beat signal to the FFT unit 23. Then, the FFT unit 23 and the Doppler frequency detection unit 24 calculate respective target velocities at a distance corresponding to each pulse.

In the coherent laser radar device according to the first embodiment, since the local light is a single pulse, the speed of a target at a single distance and the like are measured.
, A plurality of beat signals with received light from a target at a plurality of distances corresponding to n pulses of local light are obtained, and the speed and the like of the target at those distances are measured. . At that time, the delay line 11
By appropriately setting the delay time interval of each delay line 32-i and the number n of the delay lines 32-1 to 32-n in the above, speed distribution measurement or target detection measurement can be appropriately performed on the soft target.

It should be noted that a 1: n optical fiber branch (so-called star coupler) is used as the optical splitter 31 and the optical coupler 33.
By using n optical fibers having different lengths as the delay lines 32-1 to 32-n, a small delay line 11 can be obtained.

As described above, according to the second embodiment, in addition to the effects of the first embodiment, each delay line 32-1
By appropriately selecting the interval of each delay time of .about.32-n and the number n thereof, an effect is obtained in that the velocity distribution measurement or the target detection measurement can be performed on the soft target.

Embodiment 3 FIG. 7 is a block diagram showing a configuration of a delay line of a coherent laser radar device according to Embodiment 3 of the present invention. Delay line 11 shown in FIG.
In the figure, 41 is a loop line for transmitting a laser beam, and 42 is an optical coupler that introduces the incident local light into the loop line 41 and splits the light in the loop line 41.

The other components of the coherent laser radar device according to the third embodiment are the same as those according to the first embodiment (FIG. 1), and thus description thereof will be omitted.

Next, the operation will be described. FIG. 8 is a timing chart for explaining the operation of the coherent laser radar device according to the third embodiment. The target at this time is a soft target such as the atmosphere.

The optical coupler 42 introduces the pulse laser light (single pulse) from the frequency shifter 10 into the ring-shaped loop line 41. The introduced pulse laser light goes around the loop line 41. Each time the pulse laser light makes one round of the loop line 41, a part of the pulse laser light is branched off from the optical coupler 42 as local light and is incident on the optical coupler 8. As a result, local light having a pulse train whose pulse interval is the rotation time (ie, period) of the pulse laser light in the loop line 41 is incident on the optical coupler 8.

The other operation is the same as that of the first embodiment, and the description is omitted.
However, the time gate units 22 and 25 of the signal processing device 14
Extracts a beat signal corresponding to each pulse of the local light according to the time position of each pulse and supplies the beat signal to the FFT unit 23. Then, the FFT unit 23 and the Doppler frequency detection unit 24 calculate respective target velocities at a distance corresponding to each pulse.

As described above, according to the third embodiment, in addition to the effect of the first embodiment, similarly to the second embodiment, the length of the loop line 41 and the amount of branching by the optical coupler 42 are appropriately selected. By doing so, it is possible to obtain the effect that the velocity distribution measurement or the target detection measurement can be executed for the soft target.

The delay line 11 has one loop line 4
1 and the optical coupler 42, the delay line 11
Can be reduced in size.

Embodiment 4 FIG. 9 is a block diagram showing a configuration of a delay line of a coherent laser radar device according to Embodiment 4 of the present invention. Delay line 11 shown in FIG.
In the figure, reference numeral 43 denotes an optical switch for introducing a pulse laser beam into the loop line 41, and reference numeral 44 denotes an optical branch for outputting a part of the pulse laser beam as local light every time a single pulse of the pulse laser beam goes around the loop line 41 once. It is a vessel. That is, the optical coupler 42 includes the optical switch 43 and the optical splitter 44. The other components of the coherent laser radar device according to the fourth embodiment are the same as those according to the third embodiment, and thus description thereof will be omitted.

By using a photoacoustic optical element (Acousto-Optic element) as the optical switch 43, the function of the frequency shifter 10 can be provided in the optical switch 43. In that case, the frequency shifter 10 is omitted.

Next, the operation will be described. FIG. 10 shows FIG.
FIG. 5 is a diagram illustrating the operation of the optical switch of FIG. Optical switch 4
3 is opened when introducing the pulse laser light from the frequency shifter 10 into the loop line 41, and is closed after the introduction to confine the pulse laser light in the loop line 41. For example, FIG.
As shown in FIG. 0, the supplied pulse laser light is input as first-order diffracted light, and the light in the loop line 41 is changed to 0-order diffracted light. To be done.

The optical splitter 44 outputs a part of the pulse laser light as local light every time the pulsed laser light makes one round of the loop line 41. Note that the other operations are the same as those according to the third embodiment, and a description thereof will be omitted.

As described above, according to the fourth embodiment, in addition to the effect of the third embodiment, when a photoacoustic optical element is used as an optical switch, the optical switch has the function of a frequency shifter. Therefore, the effect that the device can be simplified can be obtained.

Embodiment 5 FIG. 11 is a block diagram showing a configuration of a delay line of a coherent laser radar device according to Embodiment 5 of the present invention. In the figure, reference numeral 42A is a variable optical coupler composed of an optical switch 43 and a variable optical splitter 44A, and 44A is a variable optical splitter whose branching ratio can be controlled. The other components of the coherent laser radar device according to the fifth embodiment are the same as those according to the fourth embodiment, and a description thereof will not be repeated.

Next, the operation will be described. Embodiment 3
As shown in FIG. 8, the power of a single pulse circulating in the loop line 41 decreases with each circling, so that the output of the local light decreases with time. For this reason, the S / N ratio may deviate from the shot noise limit and deteriorate as the target becomes longer.

For this reason, in the delay line 11 of the coherent laser radar device according to the fifth embodiment, the output branch ratio of the variable optical splitter 44A is controlled by a control circuit (not shown) as shown in FIG. Control so that it does not decrease constantly or rapidly. Note that the other operations are the same as those according to the fourth embodiment, and a description thereof will be omitted.

As described above, according to the fifth embodiment, the power of the pulse laser light output from the loop line 41 is kept almost constant by the variable optical splitter 44A, so that the output of the local light is Thus, it is possible to suppress the deterioration of the S / N ratio of the signal after detection due to the fluctuation of.

Embodiment 6 FIG. FIG. 12 is a block diagram showing a configuration of a delay line of a coherent laser radar device according to Embodiment 6 of the present invention. In the figure, reference numeral 45 denotes an optical amplifier provided in the middle of the loop line 41. The other components in the coherent laser radar device according to the sixth embodiment are the same as those according to the third embodiment, and thus description thereof will be omitted.

Next, the operation will be described. Embodiment 3
As shown in FIG. 8, in the coherent laser radar device according to the above, since the power of a single pulse circulating in the loop line 41 gradually decreases, the output of the local light decreases over time. Therefore, when measuring a long-distance target, the S / N ratio may be degraded.

Therefore, in order to reduce the change in the output of the local light, the optical amplifier 45 provided in the middle of the loop line 41 reduces the power of a single pulse circulating in the loop line 41 to a constant or abruptly. Amplify so as not to allow.

The other operations are the same as those according to the third embodiment, and a description thereof will not be repeated.

As described above, according to the sixth embodiment, the power of the pulse laser light in the loop line 41 is ensured by the optical amplifier 45, so that after the detection due to the fluctuation of the output of the local light. The effect of suppressing the deterioration of the S / N ratio of the signal is obtained.

In the sixth embodiment, as the optical amplifier 45, an optical fiber amplifier, a semiconductor optical amplifier, or a laser amplifier using a solid-state laser medium can be used. The effect can be obtained.

Embodiment 7 FIG. FIG. 13 is a block diagram showing a configuration of a coherent laser radar device according to Embodiment 7 of the present invention. In the figure, 50 is a delay line 11
An optical amplifier provided between the optical coupler 8 and the optical coupler 8. The other components in FIG. 13 are the same as those according to the first embodiment, and a description thereof will not be repeated.

Next, the operation will be described. In optical heterodyne detection, an S / N ratio close to the shot noise limit can be obtained by increasing the power of local light as much as possible. However, the power of local light supplied to the optical detector 12 is limited. For this reason, the S / N ratio at the time of detecting a weak reception light by setting the power of the local light as high as possible within a range not exceeding the saturation light amount which is a limit for obtaining a linear response, that is, near the saturation light amount. Higher.

FIG. 14 shows delay line 1 according to the second embodiment.
15 is a timing chart for explaining the operation of the optical amplifier 50 when the optical amplifier 1 is used, and FIG. 15 is a timing chart for explaining the operation of the optical amplifier 50 when the delay line 11 according to the third embodiment is used.

When the delay line 11 according to the second embodiment is used, the optical amplifier 50 amplifies the local light with a constant amplification factor as shown in FIG. Is supplied to the optical coupler 8. The optical coupler 8 couples the local light and the received light,
The optical detector 12 coherently detects the combined light.

Further, delay line 11 in the third embodiment
When the optical amplifier 50 is used, the optical amplifier 50 amplifies the local light by increasing the amplification factor with time as shown in FIG. 15 to make the power of the local light substantially constant near the saturation light amount, and the local light is optically coupled. To the vessel 8. The optical coupler 8 couples the local light and the received light, and forms an optical detector 12
Performs coherent detection of the combined light.

The other operation is the same as that of the first embodiment, and the description is omitted.

As described above, according to the seventh embodiment, the optical amplifier 50 is provided between the delay line 11 and the optical coupler 8, so that the coherent light with a high S / N ratio close to the shot noise limit. An effect that detection can be performed is obtained. Further, the effect of suppressing the deterioration of the S / N ratio caused by the uneven power of the local light can be obtained.

[0098]

As described above, according to the present invention, a single-wavelength pulsed laser beam is oscillated, a part of the pulsed laser beam is branched, and the pulsed laser beam is sent out toward the target. The received light is received as received light, a part of the branched pulse laser light is delayed, the delayed pulse laser light is combined with the received light, coherent detection is performed on the light, and a target physical signal is detected based on the coherent detected signal. Since the information is specified, the configuration of the device can be simplified, and there is an effect that the cost can be reduced, the size can be reduced, and the reliability can be increased.

According to the present invention, the delay means is a delay line constituted by an optical fiber having a predetermined length.
There is an effect that a small and low-loss delay means can be obtained, and the scale of the device can be reduced.

According to the present invention, the optical splitter for splitting a part of the pulse laser light split by the optical splitting means into n light beams, and the n split light beams are delayed by different delay times. Since the delay means includes the n delay lines and the optical coupler that couples the n lights delayed by the n delay lines, the velocity distribution measurement or the target detection measurement is performed on the soft target. There is an effect that can be.

According to the present invention, a loop line for transmitting laser light, a part of the pulse laser light branched by the optical branching means is introduced into the loop line, and the laser light for branching the laser light in the loop line is introduced. Since the coupler and the delay unit are provided, the velocity distribution measurement or the target detection measurement can be performed on the soft target.

According to the present invention, since the optical amplifier is provided in the middle of the loop line of the delay means, the deterioration of the S / N ratio of the detected signal due to the fluctuation of the output of the local light is suppressed. There is an effect that can be.

According to the present invention, since the optical amplifier for amplifying local light is provided between the delay means and the optical coupling means, coherent detection can be performed at a high S / N ratio close to the shot noise limit. There is an effect that can be.
In addition, there is an effect that the deterioration of the S / N ratio caused by the power of the local light being not constant can be suppressed.

According to the present invention, since the optical coupler is a variable optical coupler having a variable branching ratio, the deterioration of the S / N ratio of the signal after detection due to the fluctuation of the output of the local light is suppressed. There is an effect that can be.

According to the present invention, the optical switch of the photoacoustic optical element for outputting one of a part of the pulse laser light branched by the optical branching means and the light in the loop line to the loop line, Since the optical coupler has the optical splitter for splitting the light, the function of the frequency shifter can be given to the optical switch, and the device can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a coherent laser radar device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating an example of a configuration of the signal processing device of FIG. 1;

FIG. 3 is a block diagram showing another example of the configuration of the signal processing device of FIG. 1;

FIG. 4 is a timing chart illustrating the operation of the coherent laser radar device according to the first embodiment.

FIG. 5 is a block diagram showing a configuration of a delay line of a coherent laser radar device according to a second embodiment of the present invention.

FIG. 6 is a timing chart illustrating the operation of the coherent laser radar device according to the second embodiment.

FIG. 7 is a block diagram showing a configuration of a delay line of a coherent laser radar device according to a third embodiment of the present invention.

FIG. 8 is a timing chart illustrating an operation of the coherent laser radar device according to the third embodiment.

FIG. 9 is a block diagram showing a configuration of a delay line of a coherent laser radar device according to a fourth embodiment of the present invention.

FIG. 10 is a diagram illustrating the operation of the optical switch of FIG.

FIG. 11 is a block diagram showing a configuration of a delay line of a coherent laser radar device according to a fifth embodiment of the present invention.

FIG. 12 is a block diagram showing a configuration of a delay line of a coherent laser radar device according to a sixth embodiment of the present invention.

FIG. 13 is a block diagram showing a configuration of a coherent laser radar device according to a seventh embodiment of the present invention.

FIG. 14 is a timing chart illustrating an operation of the optical amplifier when the delay line according to the second embodiment is used.

FIG. 15 is a timing chart illustrating an operation of the optical amplifier when the delay line according to the third embodiment is used.

FIG. 16 is a block diagram illustrating a configuration of a conventional coherent laser radar device.

FIG. 17 is a block diagram illustrating a configuration example of a signal processing device of a conventional coherent laser radar device.

FIG. 18 is a timing chart illustrating an operation of a conventional coherent laser radar device.

[Explanation of symbols]

1 pulse laser, 2 optical splitter (optical splitting means), 5
Transmission / reception optical system (transmission / reception optical means), 6 scanning optical system (transmission / reception optical means), 8 optical coupler (optical coupling means), 11 delay line (delay means), 12 optical detector (optical detection means), 14
Signal processor, 31 optical splitter, 32-1 to 32-n
Delay line, 33, 42 optical coupler, 41 loop line,
42A Variable optical coupler, 43 optical switch, 44 optical splitter, 45, 50 optical amplifier.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takayuki Yanagisawa 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Electric Co., Ltd. (72) Shuzo Wadaka 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Electric Corporation (72) Inventor Etsuo Sugimoto 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Yasunori Osawa 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Rishi Electric Co., Ltd. F term (reference) 2K002 AA04 AB04 AB07 HA10 5F072 JJ01 KK15 SS06 5J084 AA05 AA07 BA03 BA11 BB14 BB16 BB21 BB31 BB35 CA03 CA48 CA61 CA64

Claims (12)

[Claims] 1. A pulse laser that oscillates a single-wavelength pulsed laser beam, and a transmission / reception optical unit that sends out the pulsed laser beam oscillated by the pulsed laser toward a target and receives light from the target as received light. An optical branching unit that branches a part of the pulse laser light oscillated by the pulse laser; a delay unit that delays a part of the pulse laser light branched by the optical branching unit; An optical coupling unit that couples a part of the pulsed laser light with the received light; an optical detection unit that coherently detects the light coupled by the optical coupling unit; and a signal that is coherently detected by the optical detection unit. A coherent laser radar device comprising: a signal processing device that specifies physical information of a target. 2. The coherent laser radar device according to claim 1, wherein the delay means is a delay line constituted by an optical fiber having a predetermined length. 3. The delay means includes: an optical splitter for splitting a part of the pulse laser light split by the optical splitting means into n light beams; and a delay device for delaying the n light beams by different delay times. 3. The coherent laser radar device according to claim 1, further comprising: n delay lines to be coupled, and an optical coupler that couples the n lights delayed by the n delay lines. 4. The delay means includes a loop line for transmitting a laser beam, a part of the pulsed laser beam branched by the optical branching unit, introduced into the loop line, and a laser beam in the loop line. 3. The coherent laser radar device according to claim 1, further comprising: an optical coupler that performs the operation. 5. The coherent laser radar device according to claim 4, wherein the delay means has an optical amplifier in the middle of the loop line. 6. An optical amplifier according to claim 1, further comprising an optical amplifier for amplifying a part of the pulse laser light between the delay unit and the optical coupling unit. A coherent laser radar device according to claim 1. 7. The coherent laser radar device according to claim 5, wherein the optical amplifier is an optical fiber amplifier. 8. The coherent laser radar device according to claim 5, wherein the optical amplifier is a semiconductor optical amplifier. 9. The coherent laser radar device according to claim 5, wherein the optical amplifier is a solid-state laser medium laser amplifier. 10. The coherent laser radar device according to claim 4, wherein the optical coupler is a variable optical coupler having a variable branching ratio. 11. An optical coupler, comprising: an optical switch of a photoacoustic optical element for outputting one of a part of the pulse laser light branched by an optical branching unit and light in the loop line to the loop line; 5. The coherent laser radar device according to claim 4, further comprising an optical splitter for splitting light in the loop line. 12. A step of oscillating a pulsed laser beam of a single wavelength; a step of branching a part of the pulsed laser beam; transmitting the pulsed laser beam toward a target; Receiving, the step of: delaying a part of the branched pulse laser light; the step of combining the delayed pulsed laser light with the received light; the step of coherently detecting the combined light; the step of coherent detection Specifying physical information of a target based on the obtained signal.